Urinary tract infection (UTI) caused by uropathogenic Escherichia coli (UPEC) is one of the most common infectious diseases in women. The morbidity and economic impact are enormous, with over $2.5 billion spent annually on treatment. Further, recurrent infections are a significant problem despite appropriate antibiotic therapy of the index case. The high rates of recurrence, and the large numbers of women that end up in urology clinics due to their chronic recurrent UTIs highlights the need for a better understanding of the pathogenic mechanisms involved in this disease and the development of new and better therapies.
Gram-negative bacteria are the causative agents of a wide variety of acute and chronic infectious diseases. Many of these infections are initiated by a critical interaction between host ligands (frequently polysaccharide moieties) and bacterial adhesins (frequently expressed at the distal tip of polymeric pilus fibers assembled by the chaperone/usher pathway). The mannose binding FimH adhesin of type 1 pili is critical for the colonization and invasion into the bladder epithelium. After invasion, UPEC are able to rapidly multiply inside superficial umbrella cells of the bladder forming biofilm-like intracellular bacterial communities (IBCs). Upon maturation, bacteria disperse from the IBC, spread to neighboring cells, and form next generation IBCs. This is the mechanism by which UPEC rapidly amplify in numbers in the urinary tract and cause disease.
The X-ray crystal structure of FimH bound to mannose showed that mannose is bound in a negatively charged pocket on FimH. The mannose binding site is highly conserved as it is invariant in 300 fimH genes sequenced from clinical UPEC strains. Thus, FimH is the critical node of the entire UPEC pathogenic cascade.
Recurrence is a serious problem for many women. Women who present with an initial episode of acute UTI have a 25-44% chance of developing a second and a 3% chance of experiencing three episodes within six months of the initial UTI. Recurrence occurs despite appropriate antibiotic treatment and clearance of the initial infection from the urine. A large percentage of recurrent UTI are caused by the same strain of bacteria as the initial infection. One study followed 58 women and found that 68% of recurrences were caused by the same initial index strain of UPEC as determined by restriction fragment length polymorphism (RFLP) analysis. In a separate study, 50% of recurrent strains isolated from female college students appeared genotypically identical to the bacterial strain corresponding to the initial UTI. Another long-term prospective study demonstrated that the same strain of UPEC can cause a recurrent UTI up to 3 years later. The high frequency of same-strain recurrences supports the notion that a UPEC reservoir can exist in the affected individual. The inventors have shown that a quiescent intracellular reservoir (QIR) can form in the bladder tissue itself after acute infection and persist even after antibiotic therapy and urine cultures become sterile. Thus, reactivation of bacteria in QIRs may also be a contributing factor in recurrent UTIs.
Therefore, there is a need for effective treatments that can cure urinary tract infections and prevent the formation of quiescent intracellular reservoir that are the source of so many recurrent infections.